The invention relates to a radar apparatus comprising transmitter means provided with a transmit generator for generating a transmitter pulse modulated at a frequency sweep rate and a reference signal modulated at the same frequency sweep rate; receiver means provided with a mixer stage for generating a heterodyne signal from the reflected transmitter pulse and the reference signal, a dispersive delay element for the frequency-dependent delay of the heterodyne signal; and a Fourier transformer unit provided with a weighting function for transforming the delayed heterodyne signal.
Such a radar apparatus is known from patent specification U.S. Pat. No. 4,912,472. This specification relates to a radar apparatus which linearly transmits frequency-modulated pulses at a 50% duty cycle, the received echo pulses being processed as is customary in a FMCW radar by mixing them in receiver means with a reference signal and subsequently digitizing, weighting and Fourier-transforming the resulting heterodyne signal. A non-simultaneous arrival of received echo pulses as a result of propagation time differences is solved by incorporating a dispersive delay element in the receiver means. Since both the echo pulse propagation time and the frequency of the heterodyne signal linearly depend on the distance between the radar apparatus and the target producing the echo pulse, a dispersive delay element of a suitably chosen dispersiveness is undoubtedly capable of compensating any propagation time differences.
A drawback of the signal processing in said radar apparatus is that any distortion of the heterodyne signal, wherever caused, may give rise, after Fourier analysis, to spurious targets.